Method of preparing refractory metals



March 1929. J. w. MARDEN ET m. 1,704,257

lmruon OF PREPARING REFRACTORY mum Original Filed Feb. 12, 1923 II I ii" I l/ VENTO J HN MARDEN THO/1 RTHOMAS JOHN E. CONLE v BY ATTORNEY JOHNWESLEY MARDEN, OI? EAST ORANGE, AND THOMAS PHILIP TH OMAS AND someEDWARD OONLEY, OF BLOOMFIELD, NEW JERSEY, ABBIGNOBB '10 WESTINGHOUSELAMP COMPANY, A. CORPORATION OF PENNSYLVANIA.

METHOD OF PREPARING REFRACTORY METALS.

Application filed February 12, 1923, Serial No. 818,544. RenewedFebruary 8, 1827.

This invention relates to methods of obtainin'g metals from theircompounds and more particularly from the diiiicultly reducible oxides ofthe rare refractory metals such as uranium, thorium, and the like.

An object of the present invention is the provision of a process for theproduct1on of metals in a high state of purity.

A further object of the invention is the provision of a process whichmay be controlled to obtain metal powders, particularly the rarerefractory metal powders, in varying degrees of fineness.

A further object of the invention is to provide a bomb in which chemicaland metallurgical operations may be practiced without the introductionof impurities from the bomb into the products produced therein.

A further object of the invention is to provide a process for protectingthe products of the reaction from becoming contaminated by impuritiesintroduced by the container in which the process is practiced.

A still further object is to provide a method of lining a bomb in anexpeditious and simple manner.

Other objects of the invention will be aparent from a reading of thefollowing speci- Ecation.

It has been proposed to obtain the powders of metals, the oxides ofwhich cannot be reduced to metal by means of hydrogen, for

example the oxides of uranium, zirconium, thorium, vanadium, tantalum,chromium, titanium, etc. or any other similarly difiiculty reducibleoxide, by the well known metallurgical processes, one of which involvedthe reduction of the oxides by means of calcium as a reducing agent.Attemptshave also been made to reduce the oxides of certain of themetals mentioned by the alkali metals, but without success. The calciummethod is open'to 0bjection because of the relative expensiveness ofthat metal and the impurities contained in the commercial material, alsobecause the heat of reaction is high which causes coarseness of thepowders through the agglomerations of the particles thereof.

In order to render effective the alkali metal reduction a furtherproposal has been made to employ an alkali metal as the reducing agent,together with a fluxing agent such as an alkaline earth halide or analkali metal halide of a metal other than the alkali metal employed asthe reducing agent. This method has been very successful, although opento several objections when it is the desire to obtain a very pure powderpossessing a certain coarseness.

In practicing the methods referred to above, it has beenv custome toinsert the mixed ingredients in an iron omb, and after sealing thelatter, the reaction is started by heating the bomb. The iron, in somemanner, finds its way into the metal produced, so that when the powderis sintered to reduce it to the coherent state, it forms, it isbelieved, with the iron, a low-melting point alloy which forms beads andruns out from the mass leaving cracks in the material and also causing agreat deal of trouble in the furnace.

Attempts have been made to prevent the introduction of the iron impurityby lining the bomb with nickel, copper, chromium, etc., but in eachcase, metallic impurities were introduced ,which were most undesirablein preparing pure metals.

To illustrate the effect on the physical properties of a metal by theintroduction of a small amount of an impurity, reference need only bemade to the effect of carbon or any metallic impurity in pure iron. Forexample, .a small amount of silicon or carbon, when introduced intoiron, causes the latter to become hard and brittle. The same effect willprobably be produced if instead of iron, say uranium or thorium, wereused. From our experience. with the rare refractory metals and theirpreparation, we are convinced that when iron is present as an impurity,it is very difficult to obtain the metal with which it is combined in asolid coherent condition owing to the beading previously referred to.

Therefore, in order to provide a process which may be practiced toobtain the rare refractory metal powders in avery pure state and of apredetermined degree offineness, the following method has been devised.

In practicing our invention we employ as the reducing agent an alkalineearth metal, preferably calcium, and employ as the fluxin agent a halideof the same alkaline cart I metal being inabout 50% excess of thetheoretical quantity required. This mixture is heated in a suitablevessel, preferably a bomb, which is evacuated or provided with any othersuitable inert environment from which nitrogen and oxygen are absent.

In the accompanying drawing 1s;1llustrated a vertical sectional view,partly in elevatipn,

of a bomb provided with an insulating hnmgof calcium oxide, within whichthe charge is placed. The bomb comprises a hollow iron cylinder 2 havinga chamber 3 within the same. The bomb may be about 10 inches in heightand 4 inches in diameter with a wall thickness of approximately a halfinch. The upper end 4 of the bomb is provided with an internal taperedthread 5 'into which fits a tapered threaded plug 6 to the threads ofwhich a sealing compound may be applied just previous to the insertionof the plug into the bomb. The inner walls of the chamber 3 in the bombare referably provided with an insulating layer of calcium oxide orother satisfactory material which may preferably be applied in a mannermore fully described hereinafter. I

In placing the mixture into the bomb, we observe the followingprecautions in order to prevent the introduction of impurities from thebomb. The bottom 8 of the bomb is covered with a layer 9 of pure,specially prepared highly ignited lime which contains no iron, silicon,or insoluble impurities. By insoluble impurities we mean insoluble indilute acetic acid. After the bottom of the bomb has been covered abouta quarterinch deep by thoroughly packing with a clean iron plunger, themixture of calcium chloride, finely cut calcium, and the rare refractorymetal oxide is pressed into cakes 11 somewhat smaller than the inside ofthe bomb. A cake is placed centrally on the lined bottom of the bomb andlime powder 12 is run in around the cake and packed down with a cleancopper oriron ring. Usually,,three or four cakes are pressed and put in,one at a time, the lime being packed around each one of them after itsintroduction within the bomb, so that the final formation comprises aninsulating layer of the lime interposed between the mixture and thewalls of the bomb. A piece 13 of calcium is placed upon the uppermostcake to combine with the residual air remaining in the bomb or materialswithin the same. The bomb is then sealed by inserting the plug 6 afterhaving previously applied a sealing mixture of magnesium oxide andlinseed oil thereto. The bomb may be evacuated or provided with an inertenvironment, although we do not find this necessary as the lump ofcalcium removes the residual air. The reaction is then started by theexternal application of heat.

After the reaction is complete and the bomb permitted to cool, thecontents thereof may be removed by means of a star drill which is smallenough so'that it does not touch the sides of the'bomb at any time andwhich has a stop on the handle so that the drill cannot come closer thanof the bottom. In that way practically all of the charge is removed, butno iron is knocked loose from the bomb mechanically and practically nocorrosion can take place or iron be introduced since there is no contactbetween thespecimen and the metal of the bomb.

.We may also, if the bomb and the contents are kept cool, disintegratethe charge with water, which process avoids the necessity of 7 cuttingloose the charge with a drill. In practicing this method of removal,considerable care should be exercised to have the bomb and contentscool, otherwise the rare metal powder, particularly in the case ofuranium, will interact with the hot water and thus destroy the formerspurity.

The contents of the bomb upon removal may be treated in any' well knownmanner to remove the undesirable products of the reaction. For example,such purification may consist of washing with dilute acid, water, etc.so that only the pure metal powder remains.

We believe that by practicing the foregoing method more nearly idealconditions prevail for the production of pure metal powders for thefollowing reasons: First, the alkaline earth metal halide may, withcertain refractory oxides,'serve as a flux so that the oxide isconverted to the chloride, partially at least, where it is readilyreduced. Second, the pow der which is formed usually settles to thebottom of the fused mass so that the fluid calcium chloride would veryeffectually seal it away if any leakage in the bomb occurred after thereduction of the metal. Third, the calcium chloride serves as a mediumso that the calcium and the oxide come very intimately into contact.Thereduction, therefore, .by this method, is very complete. Fourth, thealkaline earth metal halide or flux material slows up the reduction andthus provides a means for the regulation of the coarseness of the powderby the excess of the fluxing agent, so that when the temperature ofreduction and the excess of reducing agent are once determined, apractically 100% yield of the metal powder may be obtained withoutlosing any large amount of it, which would necessarily have to'bescreened away on account of it being too coarse to press. By followingthe method outlined, we have found that the temperature and amount offiux material may be regulated within certain limits so that successivepreparations of the powder give uniform results. I y

In applicants copending application, Serial No. 504,154, filed September29, 1921, assigned to the present assignee, reference is purpose.

To enable those skilled in the art to practice our invention, we willdescribe, in detail,

one method of applying the principle in-' volved, and, for this purpose,will select uranium oxide as an example of a diflicultly reducibleoxide, calcium as the alkaline earth metal or reducing agent, andcalcium chloride as the alkaline earth halide or fluxing agent.

An intimate mixture is prepared in any suitable manner of 92 parts byweight of uranium oxide (U 0 or under slightly differing conditionsequivalent quantities of the other oxides of uranium, a large excess(120 parts by weight) of calcium prepared from purifier calciumchloride, and a suitable uantity or about 200 parts by weight ofpurifled calcium chloride. The calcium chloride purchased as chemicallypure and labelled calcined contains water, and in practicing our processwe prefer to carefully dry the same at about 450 C. or at a highertemperature, so that it contains only a few tenths of one percent ofmoisture. If the commercial calcined calcium chloride is used, then itis necessary to employ an excess of calcium to combine with the oxygen.It is desirable to have very pure materials, since a small amount ofiron for example, appears to cause beading due to the formation oflow-melting point alloys, etc. Silicon also makes the metal hard andbrittle:

The mixture is pressed into cakes somewhat smaller than the bomb intowhich they are placed. A lining of pure calcium oxide is placed aroundthe cakes in the manner heretofore described, after which the bomb issealed. The bomb may then be evacuated or provided with an inertenvironment, or in lieu of this treatment a lump of calcium may beplaced on top of the charge, prior to sealin g o l the bomb, tocombinewith any residual air remaining within the same. External heat isapplied to raise the temperature of the bomb to a bright red heat orabout 900 C. to 1000 C. and this temperature is maintained from two tothree hours. The temperature limit to which the'bomb is heated dependsupon the actual proportion of calcium and calcium chloride used and uponthe duration of heating. Definite instructions concerning this matterare not given for the reason the proportions and duration of heatingmust be varied with different grade oxides, which are used. For example,uranium oxide having the chemical formula U0 takes a differenttemperature, excess of reagents and time of heating than is required forthe oxide having the formula U 0 After the completion of the reaction,the products are allowed to cool and are then removed from the containerby means of a drill or the charge is simply disintegrated with water asabove indicated. The mass is treated in any desired manner well known toone skilled in the art to eliminate all but the uranium owder.

The fol owing procedure has been followed in treatin the products of thereaction to remove all but the rare refractory metal powder. water, thelatter being constantly stirred so as to bring about a more intimatecontact with the mass. After settling, the supernatant liquor isdecanted, and the residue washed with fresh water. The washing treatmentis. repeated several times after which dilute acetic acid is added tothe residue to remove matter soluble therein. The residue is then washedwith water and the residue again acidified as before. The acid and waterwashing treatments are repeated about four times after which the residueis put through a. suction filter and washed with distilled water. Thedistilled water washing in the filter is followed by washing withalcohol. The powder is partially dried by suction and it is then quicklyput through a 200 mesh screen a little at a time. If the powder isexposed to the air for a short time,'it frequently spontaneously ignitesand is burned to oxide so that this must be done quickly. The powder ispreserved by being'placed in pure alcohol. Before forming the powderinto a slug for treatment in accordance with the metallurgical processdescribed in the application of John W. Marden and H. C. Rentschler,Serial No. 432,325, filed December 21, 1920, and assigned to theWestinghouse Lamp Company, it is given the acid-wash treatment describedin the application of John W. Marden, Serial No. 583,376, filed August21, 1922, and assigned to the Westinghouse Lamp Compan T e powder thusproduced readily passes the 200 mesh sieve and can be pressed into hardsolid cakes having much the appearance of molybdenum under the sameconditions. It might be stated that when the powder is too fine it canbe filtered only with difficulty and when pressed squeezes out at thesides of the press. When the powder is too fine,it is extremelydifficult todegasify in the furnace since t e large volume of gas causescracks to be produced even when extreme care is exercised. It is usuallynecessary to press and handle pure uranium powder wet with alcohol inorder to avoid spontaneous combustion in the air. Also a powder which istoo fine shrinks to a large extent in the furnace. yielding misshapenslugs or buttons. 1 When a powder is too coarse it does not holditsshape after pressing, but crumbles and can be handled only withdifficulty.

Many other methods may be followed in lining the bomb. For instance, thelining material may be ressed around a core, which latter may be witdrawn, or it may be wetted and painted in. Obviously other materials u io o The mass is allowed to disinte rate 1n gen chloride, thus avoidingthe use of water may be employed as the lining material, for example,strontium oxide. owever, it should be remembered that the materialemployed or the method followed in lining the bomb with the same shouldbe such as to avoid the introduction of impurities.

If so desired, when calcium and calcium chloride are used as reducingagents, it is possible to completely remove the undesirable products ofthe reaction and the excess of reducing agents by means of pure alcoholand a solution of an acid in alcohol such as hydroand contamination duethereto.

In practicing our process we emphasize the im 'ortance of em loying purematerials in or er to obtain tlie pure refractory metal powders.Therefore, such precautionary measures may be taken, as practice maydictate, of eliminating, as far as is practically possible, from thematerials, such as the oxides, the calcium, the calcium chloride, thecalcium oxide, and other reagents, any impurities, such as iron, freecarbon, carbides, etc., which ma be present therein and which mayoperate etrimentally in reducing the refractory metal powder to thehomogeneous coherent condition by heat treatment in the vacuum furnacedescribed in the copending application of Harvey C. Rentschler, SerialNumber 430,118 filed December 13, 1920, and assigned to the WestinghouseLamp Company.

Modifications of the process described above may occur to those skilledin the art, but such as fall within the scope of the appended claims arecontemplated by us as forming part of our invention."

What is claimed is:

1. The method of producing rare refractory metals such. as uranium,thorium and the like from their diflicultly reducible oxides whichcomprises heating to a reacting temperature such oxides, an alkalineearth metal and an alkaline earth halide.

"2. The method of producing rare refractory metals such as uranium,thorium and the like from their difiicultly reducible oxides whichcomprises heating to a reacting temperature such oxides, an alkalineearth metal and an alkaline earth halide, the base of which is-the sameas the alkaline earth metal employed.

and calcium.

6. The method which comprises forming a mixture of uranium oxide, andalkaline earth halide and an alkaline metal, enclosing said mixture in abomb, excluding oxygen and nitrogen from said bomb, raisin the mixtureto reaction temperature, permitting the bomb to cool, and then treatingthe reaction pro'ducts to eliminate all except the uranium.

7 The method of producing uranium powder of any degree of fineness whichcomprises forming a mixture of any uranium oxide such as U0 an alkalineearth halide and an alkaline earth metal, the proportions of the lastnamed ingredient'being in about 50% excess of the theoretical quantityrequired, placing the mixture in 'a bomb, excluding oxy n and nitrogenfrom said bomb, heating the mb to a red heat for about two hours,permitting the bomb to cool and treating the reaction products toeliminate all but the uranium powder.

8. The method of producing uranium powder of any degree of finenesswhich comprises heating to a reacting temperature an oxide of uranium,calcium and calcium chloride in predetermined excess proportionsandapplying heat for a predetermined period depending upon the fineness ofpowder desired and the particular oxide of uranium used.

9. The method of reducing diflicultly reducible oxides of refractorymetals which comprises heating the oxide of a refractory metal in thepresence of a halide to convert the oxide to a halide and simultaneouslyreducing the halide thus formed.

I 10. The method of reducing the diflicultl reducible oxides ofrefractory metals whic comprises heating to a reacting temperature, anoxide of a refractory metal and an alkaline earth halide to convert theoxide to arefractory metal halide and simultaneously converting thehalide to metal by means of cal- 0mm.

11. The method of reducing the difiicultl reducible oxides of refractorymetals whic comprises heating to a reacting temperature, an oxide of arefractory metal and calcium chloride to convert the oxide to refractormetal chloride, rendering inefi'ective such products of the reactionwhich prevent the reduction from going to completion and simultaneouslreducin the refractory metal halide thus ormed bylieating the same inthe presence of calcium.

12. The method of reducing the difiicultl reducible oxides of refractorymetals whic comprises heating to a reacting temperature,

an oxide of the refractory metal, a converting agent capable ofconverting the oxide to a halide and also capable of removing reactionproducts which retard further conversion, and a reducing agent capableof reducuranium powder by reduction of an oxide ing said refractorymetal halide which is thereof inabomb, which consists in surroundformedduring the reaction. ing the charge with an insulating layer of 13. Thestep in the production of pure rare calcium oxide.

5 refractory metal powders by reduction of the In testimony whereof, wehave hereunto oxides in a bomb which consists in insulating subscribedour names this 10th day of Febthe charge from the walls of the bomb byruary,1923. interposing a layer of calcium oxide between JOHN WESLEYMARDE'N. the charge and, the walls of the bomb. THOMAS PHILIP THOMAS.

10 14. The step in the production of pure JOHN EDWARD CONLEY.

